The present invention relates to a method and an apparatus for patterning tapes or foil strips. In particular, the present invention is directed to continuously patterning a photosensitive tape for use as a film carrier for integrated circuit chips.
Up to a few years ago, wire-bonding was the most commonly used method for making connections from an integrated circuit (IC) chip to the outside world. An alternative to wire-bonding consists of using a tape carrier, similar to a movie film, having lead frames formed along its surface. In this film-carrier approach, usually a polyimide film carries a copper lead pattern that repeats itself along the length of the film. The finger-like leads of an individual site on the film are bonded simultaneously to the pads of an IC chip, as for example, described in U.S. Pat. No. 3,689,991 to A. D. Aird, issued Sept. 12, 1972, and U.S. Pat. No. 3,968,563 to A. H. Hamlin, issued July 13, 1976.
These two known processes make use of a thin strip of a continuous electrically insulating tape having a plurality of prepunched apertures at regularly spaced intervals. A thin foil-like strip or layer of electrically conducting material is secured to the tape. By photolithographic masking and etching, portions of the layer are removed to form a plurality of sets of metallic finger-like leads. This subtractive technique, used to form the finger-like leads, is described in an article by S. E. Grossman entitled "Film-carrier Technique Automates the Packaging of IC Chips" in Electronics, May 16, 1974, pages 89-95. According to this article, the technique consists in first bonding a 1-ounce copper foil to a polyimide film by means of an adhesive. Photoresist techniques form the image of the desired lead frame in a step-and-repeat fashion along the film-mounted copper laminate. This step-and-repeat projection requires indexing, settling and alignment, all of which are time-consuming and expensive operations. Moreover, such a projection technique is difficult if long lengths of tapes are needed since accelerations associated with high speed indexing are damaging to the fragile tape. Furthermore, the high price-per-pound of the polyimide carrier increases the cost per site of such a tape especially when small quantities of custom tapes are needed.